The factors underlying the large interindividual variability in response to glucocorticoids in Giant Cell Arteritis are poorly understood. The investigators hypothesize that a part of this variability is related to pharmacokinetic factors determined by genetic polymorphism: hepatic clearance involving cytochromes P450 of the subfamily 3A (CYP3A) and drug efflux leukocyte conditioned by P-glycoprotein involved in multidrug resistance drugs (ABCB1). The investigators have designed a multicentric prospective pharmacokinetical and pharmacogenetic cohort study to assess the link between prednisolone clearance and the relapse risk in giant cell arteritis.

Prednisone therapy delivered in accordance with a 10 to 18 month pre-defined schedule. Pharmacokinetic and pharmacogenetic tests at 14 or 28 days. Monthly visit for the first 6 month, then every 8 weeks months thereafter for the remainder of the study with standard biologic monitoring , physical exam and medical and medication history .Also, participants will be asked to complete several questionnaires to assess quality of life and observance to therapy. Participants may have additional study visits if a disease flare or disease-related complications occur during the study.

Eligibility

Ages Eligible for Study:

50 Years and older (Adult, Senior)

Genders Eligible for Study:

Both

Accepts Healthy Volunteers:

No

Criteria

Inclusion Criteria:

Diagnosis of GCA, meeting at least 3 of the following 5 American College of Rheumatology (ACR) criteria for the diagnosis of GCA:

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Please refer to this study by its ClinicalTrials.gov identifier: NCT01400464